Bethesda isn't making the firmest stand against Sony's policies, since other games like Fallout 76 are still destined for the PS4. It's doing this because Legends' cross-play is a selling point, and because a card game doesn't need the performance of a living room console.
However, it's telling that the developer is willing to forego sales on a strong-selling console just to ensure that a game lives up to its vision. And that may be a concern both for Sony and gamers. It's one thing when PS4 owners have to play a game solely within their own ecosystem, but it's another when certain games aren't available at all on your platform of choice. While it's unlikely that you'll see a mass exodus from the PS4, this suggests that other big studios might skip the system for other releases that depend on cross-play to succeed. In that light, Sony's talk of a possible 'solution' for cross-play limitations can't come soon enough for gamers who want access to as many titles as possible.